<!DOCTYPE html>
<html>

<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        .wrap {
            width: 300px;
            margin: 100px auto 0;
        }

        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
            width: 300px;
        }

        th,
        td {
            border: 1px solid #d0d0d0;
            color: #404060;
            padding: 10px;
        }

        th {
            background-color: #09c;
            font: bold 16px "微软雅黑";
            color: #fff;
        }

        td {
            font: 14px "微软雅黑";
        }

        tbody tr {
            background-color: #f0f0f0;
        }

        tbody tr:hover {
            cursor: pointer;
            background-color: #fafafa;
        }
    </style>

</head>

<body>
    <div class="wrap">
        <table>
            <thead>
                <tr>
                    <th>
                        <input type="checkbox" id="j_cbAll" />
                    </th>
                    <th>商品</th>
                    <th>价钱</th>
                </tr>
            </thead>
            <tbody id="j_tb">
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPhone8</td>
                    <td>8000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPad Pro</td>
                    <td>5000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>iPad Air</td>
                    <td>2000</td>
                </tr>
                <tr>
                    <td>
                        <input type="checkbox" />
                    </td>
                    <td>Apple Watch</td>
                    <td>2000</td>
                </tr>

            </tbody>
        </table>
    </div>
    <script>
        //1.全选和取消全选
        var j_cbAll = document.querySelector('#j_cbAll');
        var j_tbs = document.querySelector('#j_tb').querySelectorAll('input');


        j_cbAll.onclick = function () {
            for (var i = 0; i < j_tbs.length; i++) {
                j_tbs[i].checked = this.checked;
            }
        }

        //下面控制上面
        for (var i = 0; i < j_tbs.length; i++) {
            j_tbs[i].onclick = function () {
                var cnt = 0;
                for (var j = 0; j < j_tbs.length; j++) {
                    if (j_tbs[j].checked == true) {
                        cnt++;
                        console.log(cnt);
                        if (cnt == j_tbs.length) {
                            j_cbAll.checked = true;
                        }else{
                            j_cbAll.checked = false;
                        }
                    }
                }

            }
        }



    </script>
</body>

</html>